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Dr. Stephen Green

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2.04

Main Focus

I have broad interests in gravitational physics, including
astrophysics and gravitational wave observations, and more theoretical
questions.

In astrophysics, I have recently become interested in
using gravitational wave observations of neutron star binaries to
extract information about their internal structure. Indeed, the
deformability of the stars due to the tidal forces they exert on each
other is sensitive to the equation of state of the interior, and this
imprints on the waveform. There are various tidal effects at different
multipole order, and those that couple to neutron star spin, they all
appear to have universal behavior together with other internal-structure
dependent properties. I would like to understand the origin of this
behavior. I am also interested in gravitational-wave data analysis.

My
more theoretical interests are in stability problems and nonlinear
dynamics in general relativity, often in the context of asymptotically
anti-de Sitter (AdS) spacetimes. These spacetimes are of holographic
interest in high energy physics, and they can also exhibit complex
nonlinear dynamics such as turbulence in the geometry. The latter occurs
because asymptotically AdS spacetimes confine gravitational waves,
reducing dissipation so nonlinear effects can take hold. A major
question I have worked on is to determine the final state of small
perturbations of AdS, a problem which is holographically dual to the
thermalization of strongly coupled field theories. The interesting
dynamics that occur may also manifest in the vicinity of near-extreme
black holes, and I would like to study their implications for
astrophysics.

For my PhD, I studied general relativistic effects
in cosmology. I constrained possible nonlinear backreaction effects that
had been suggested by others as an alternative to dark energy, and I
demonstrated the effectiveness of Newtonian cosmological simulations as
an approximation to general relativity.

Curriculum Vitae

I completed my PhD in physics at the University of Chicago in 2012. My dissertation, supervised by Robert Wald, constrained nonlinear backreaction effects in relativistic cosmology. After graduating, I became a CITA National Fellow at the University of Guelph, Canada, and later a postdoctoral researcher at the Perimeter Institute. At these places I worked on stability problems and turbulence in general relativity using both mathematical and numerical approaches. Since September 2017 I have been a postdoc at the AEI in Potsdam-Golm, joint between the Astrophysical and Cosmological Relativity and the Quantum Gravity and Unified Theories divisions.